// global object
var a = [1, 2, 3];
var date = new Date();
date.getTime();
var reg = /abc/;
reg.test("acsd");
// build-in object
Math.pow(2, 2);
// DOM and BOM
var body = document.body;
// body.append()
var allLis = document.querySelectorAll('li');
// allLis.keys()
document.addEventListener('click', function (e) {
    e.preventDefault();
});
var viking = { name: "viking", age: 12, des: "my name viking", student: true };
var viking2 = { age: 12 };
var viking3 = { age: 12, student: false };
